This invention relates to a driving circuit which drives a liquid crystal display panel of active matrix type in response to a picture signal so as to display an expanded picture.
Recently, a flat panel display is often used for a display device of a personal computer, an audiovisual equipment, etc. Generally, a liquid crystal display (LCD) is known as the flat panel display.
The liquid crystal display is considerably thinner than a CRT display which has the same size screen. Moreover, the liquid crystal display is considerably lower than the CRT display in electric power consumption. Thus, the liquid crystal display is more attractive than the CRT display.
By the way, it is necessary that the liquid crystal display can deal with various kinds of standardized picture signals like the CRT display in order to generalize the liquid crystal display. In other words, the liquid crystal display must be able to display various pictures which has various standardized resolution.
Resolution of the liquid crystal display is decided by the number of pixels. Accordingly, the number of pixels is decided in consideration of the highest resolution of standardized picture signals displayed on the liquid crystal display. In this case, the number of the pixels is equal to the number of picture data of each frame of the picture signal.
When the number of the picture data is smaller than the number of the pixels, the liquid crystal display must interpolate the picture data in each frame to expand an original picture which corresponds to the picture signal.
A conventional driving circuit has a special signal processor so as to expand the original picture. The special signal processor defines a plurality of drive frames each of which differs from each picture frame and which includes interpolated data in addition to a picture signal of each picture frame. The conventional driving circuit displays both the picture signal and the interpolated data on a liquid crystal display panel within each drive frame.
However, the special signal processor is required to produce the plurality of drive frames from each frame of the picture signal in the conventional driving circuit. Moreover, very complicated control is needed to display the plurality of frames in the conventional driving circuit.
Another conventional driving circuit has a clock multiply circuit which multiplies a system clock signal to produce a multiplied system clock signal. The conventional driving circuit samples a picture signal by use of the multiplied system clock signal to produce a picture data which is equal to the pixels in number.
However, the conventional driving circuit can deal with an analog picture signal but can not deal with a digital picture signal.